(1) Field of the Invention
The present invention relates to a display device and a method of manufacturing the same, and in particular, to a display device having a repairable pixel structure and a method of manufacturing the display device.
(2) Description of the Related Art
Organic electroluminescence (EL) displays including organic electroluminescence elements (hereinafter referred to as organic EL elements) are known as image display devices including current-driven luminescent elements. The organic EL displays are attracting attention as a candidate for next-generation flat panel displays (FPDs) because they are viewable at wide angles and consume a small amount of power.
Usually, organic EL elements included in pixels are arranged in a matrix pattern. For example, in active-matrix organic EL displays, thin-film transistors (TFTs) are provided at intersections of scanning lines and data lines, and each TFT is connected with a capacitor (capacitor) and the gate of a driving transistor. The TFT is turned on through a selected scanning line to allow a data signal to be provided to the driving transistor and the capacitor through a corresponding data line so that the driving transistor and the capacitor control the timing when the organic EL element produces a luminescence. With this configuration of the pixel controller, the active-matrix organic EL displays can cause the organic EL elements to keep producing luminescence until next scanning (selection), and thus there is no reduction in the display luminance even when the duty ratio increases. However, as typified by the active-matrix organic EL displays, when the complexity of the controller configuration of the luminescent pixels increases or when the number of luminescent pixels increases, electrical troubles, such as a short circuit and/or an open circuit of circuit elements and transmission lines, are more likely to occur during a manufacturing process which requires fine processing.
With organic EL panels, in particular, the capacitors included in the pixel controllers have a relatively wide element area. Consequently, the capacitors are susceptible to a particle or the like present between electrodes, thereby causing a higher percent defective of pixels through a short circuit.
Meanwhile, there is a method proposed for repairing a defective luminescent pixel after forming pixel controller elements and transmission lines. In order to repair a defective luminescent pixel which has become a bright point in a constant luminescent status due to a short circuit of a circuit element or the like, Japanese Unexamined Patent Application Publication No. 2008-203636 (hereinafter referred to as Patent Reference 1) provides, in each of the luminescent pixel regions, a non-overlap portion connected to other conductive portions and transmission lines with some distance therefrom. To repair a defective luminescent pixel, the non-overlap portion is disconnected by laser irradiation. With this, transmission of electric signals to the defective luminescent pixel is blocked. Moreover, the defective luminescent pixel becomes a dark point without any damage from the laser irradiation.
Furthermore, in Japanese Unexamined Patent Application Publication No. 2007-66904 (hereinafter referred to as Patent Reference 2), a pixel electrode formed in a luminescent region of each luminescent pixel is provided by connecting cells, so that by disconnecting a cell connection with a laser, only the defective luminescent cell is electrically insulated and becomes a dark point.
In order to increase density of pixels according to the increase in the number of luminescent pixels for enhanced-definition of display panels, it is necessary to devise, particularly, a layout of capacitors having a higher area ratio. The effective solution is that capacitors function as both the originally-given capacitance elements and transmission lines for connecting circuit elements to each other (hereinafter also referred to as a transmission-line function).
However, when a current-leaking portion is to be repaired with a laser or the like with the structure described in Patent Reference 2 while the capacitors function both as the capacitance elements and the transmission lines, in order to deal with a shorted circuit of the capacitor, which is the main cause of defective pixels, the transmission lines are frequently disconnected depending on a short-circuited portion. If so, the transmission-line function is lost. As a result, although the defective luminescent pixel can become a dark point, it cannot restore the function as a normal luminescent pixel.
Furthermore, although the structure and method described in Patent Reference 1 can make the capacitor electrically insulated from the other circuit elements so that the capacitor is disabled, there is a limitation on arranging all the capacitors as non-overlap portions connected to other conductive portions and transmission lines with some distance therefrom to devise the layout of the capacitors for increasing the density of pixels according to the increase in the number of luminescent pixels.
Even when the defective luminescent pixel can become a dark point or the organic EL element produces a luminescence at different timing of the other normal luminescent pixels according to any of the prior arts, it is not possible that the defective luminescent pixel produces the luminescence at the same timing as the normal luminescent pixel to improve the display quality of the luminescent panel.
The present invention, conceived in view of the above problems, has an object of providing (i) a display device that enables a defective luminescent pixel including a short-circuited capacitor to produce a luminescence with proper luminescent timing and (ii) a method of manufacturing the display device, even when the density of pixels increases.